Flame arrestor

ABSTRACT

A flame arrestor for a flowing explosive gas ( 4 ), having a flame barrier ( 10, 20, 30 ) with a large number of defined passage gaps ( 17, 18 ), whose gap cross section is set with regard to the properties of the flowing gas ( 4 ), is cooled effectively and secured against a flame flashback in the case of continuous combustion by the fact that second gaps ( 18 ) having a smaller gap cross section are arranged adjacent to the first gaps ( 17 ) having the selected gap cross section.

The invention relates to a flame arrestor for a flowing explosive gas,having a flame barrier with a large number of defined passage gaps,whose gap cross section is set with regard to the properties of theflowing gas.

Flame arresters of this type are used, for example, for the ventilationof plant at risk of explosion. They must be designed to be safe withrespect to continuous combustion in the event of ignition of the gas orproduct vapor-air mixtures flowing out, that is to say it must bepossible to flare off the gas/gas mixture over an unlimited time periodwithout a flame flashback into the part of the plant to be protectedoccurring.

The flame arresters are based on the principle that the gas flowingthrough the passage gaps of the flame barrier is cooled by the wall ofthe passage gaps, so that the gas at the outlet of the flame barrier iscooled below its ignition temperature. In order to achieve safety withrespect to continuous combustion, the material of the flame barrierwhich bounds the passage gaps must be cooled adequately in order thatthe intended cooling of the gas on the wall of the passage gaps isachieved.

The maximum heating of a flame barrier arises if the flow reaches orfalls somewhat below what is known as the critical volume flow in theflame-extinguishing gaps. The critical volume flow corresponds to a flowvelocity which corresponds to that of a laminar propagation velocity tobe assigned in each case to every ignitable mixture. In this operatingstate, the gas or the gas mixtures not only flare immediately on thesurface of the flame barrier but initially penetrate somewhat into theflame-extinguishing gap. Since, as a result, the wall of theflame-extinguishing gap is heated up, the flame can penetrate deeper anddeeper into the flame-extinguishing gap, which means that there is arisk of flame flashback.

FIG. 1 shows a known flame arrestor, which is arranged so as to besecure against continuous combustion at the outlet of a part of a plant.It comprises a housing 1 having a flange 2 on the plant side and aconical widening 3 oriented away from the flange 2 and belonging to aflow duct 4, which is terminated at the other end of the housing 1 by aflame barrier 5. The flame barrier 5 comprises turns 6 wound in acircular or spiral shape, which are preferably produced by thecombination of a smooth metal strip with a corrugated metal strip. Thegap cross section is defined by the choice of the corrugation of thecorrugated metal strip. The width of the metal strip determines the gaplength. FIG. 1 shows that the gas flowing through the flame barrier 5has ignited on the side facing away from the plant and forms flames 7.

The detail A illustrated in FIG. 2 shows the penetration of the flames 7into the gaps 6 in an enlarged illustration. It is therefore necessaryto ensure on the plant side that a flow velocity for the gas is alwaysmaintained which prevents the flow falling below the critical volumeflow. This may be achieved in principle by the cross section of the gapsbeing reduced since, as a result, the volumetric velocity of the gas inthe gaps is increased. However, this enlarges the flow resistanceeffected by the flame barrier. In order to achieve the same total freecross section, the area of the flame barrier, that is to say the conicalwidening 3 of the flow duct 4, must be enlarged for this purpose. Thismeans that the flame arrestor becomes more voluminous and moreexpensive.

The present invention is based on the object of constructing a flamearrestor of the type mentioned at the beginning with increased safetywith respect to flame flashbacks.

In order to achieve this object, according to the invention a flamearrestor of the type mentioned at the beginning is characterized in thatsecond gaps with a smaller gap cross section are arranged adjacent tothe first gaps having the selected gap cross section.

The present invention is based on the effect that, for the case in whichthe critical volume flow is reached for the first gaps, the flowvelocity in the second, narrower gaps, is still considerably higher, sothat adequate cooling by the flowing gas is in any case carried out inthe narrower, second gaps. The cooler gaps are then capable of pickingup and carrying away heat from the adjacent first gaps. The flowresistance of the flame barrier is increased only little overall by thenarrower second gaps, so that an enlargement of the total area of theflame barrier is not required or is required only to a low extent. Onaccount of the action described of the second gaps, a considerableimprovement of the security against flame flashback of the flame barrieris achieved with a design which is otherwise unchanged.

In a preferred embodiment of the invention, the passage gaps areimplemented in a disk-like flame barrier, the gaps preferably beingarranged on turns formed in the shape of rings or spirals.

The arrangement of the second gaps relative to the first gaps can becarried out in a simple manner by a first number of turns having firstgaps and a second number of turns having second gaps being providedalternately. In this case, it is conceivable for the first number andthe second number both to be 1, so that in each case one turn havingfirst gaps and one turn having second gaps are provided. However, forspecific applications, it is also expedient, for example, to provideonly each third turn with narrower second gaps, so that in each case twoturns having first gaps are arranged between two turns having the secondgaps.

Conversely, the approach can be to have a turn having first gapsfollowed in each case by two turns with second, narrower gaps.

The ratio of the number of turns having second gaps to the number ofturns having first gaps can be constant over the area of the flamebarrier. In the case of flat flame barriers, in particular those whichhave turns formed in the shape of rings or spirals, it can beparticularly expedient if the ratio of the number of second gaps to thenumber of first gaps varies over the area of the flame barrier, inparticular if the ratio of the number of second gaps to the number offirst gaps decreases from the inside to the outside. This structure ofthe flame barrier is based on the finding that disk-like flame barriersheat up most intensely at the center of the flame barrier, so that thecooling action of the second, narrower gaps can be used to an increasedextent there.

In the case of turns formed in the shape of rings or spirals, therefore,the relative number of turns having the second gaps can be greater inthe center of the flame barrier than in the outer region.

The turns of the disk-like flame barrier are preferably formed by acorrugated metal strip wound spirally together with a smooth metalstrip, a first corrugated metal strip having larger corrugations formingthe turns having the first gaps, and a corrugated metal strip havingsmaller corrugations forming the turns having the second gaps.

The second gaps can all have the same gap cross section. However, it isalso possible for the second gaps to have at least two different gapcross sections, that is to say for smaller gap cross sections ofdifferent magnitude to be used in conjunction with the first gaps. Forfabrication reasons, however, providing only one gap cross section forthe second gaps will regularly be preferred.

The implementation of the first and second gaps can also be carried outby the turns having the first and second gaps over their length, sothat, over the length of the turns in each case, a first number of firstgaps and a second number of second gaps are arranged alternately oneafter another.

In the preferred embodiment of a disk-like flame barrier which is formedby a corrugated metal strip wound spirally together with a smooth metalstrip, the corrugation of the corrugated metal strip thus alternatelyhas shorter and longer lengths of the corrugations in order to form thefirst and second gaps.

In the flame barriers according to the invention, the first and secondgaps are preferably formed with the same gap lengths.

The cross-sectional area of the second gaps should amount at most to thesize of the cross-sectional area of the first gaps, in order to achievethe effect according to the invention clearly enough. The selection ofthe cross-sectional area of the second gaps, however, is naturallyassociated with the selected number of the second gaps relative to thenumber of the first gaps. From this, those skilled in the art are givena not inconsiderable freedom of configuration within the scope of thepresent invention. The ratio of the cross-sectional area of the second(narrower) gaps to the cross-sectional area of the first (wider) gaps ispreferably between 25 and 50%, preferably around ⅓ to ⅔.

The invention is to be explained in more detail in the following text byusing exemplary embodiments illustrated in the drawing, in which:

FIG. 1 shows a longitudinal section through a flame arrestor having aconventional flame barrier

FIG. 2 shows a detail from FIG. 1 in order to illustrate theconstruction of the conventional flame barrier

FIG. 3 shows a perspective view of a first embodiment of a flame barrieraccording to the invention for use in a flame arrestor according to FIG.1

FIG. 4 shows an enlarged detail B from FIG. 3 in order to illustrate theconstruction of the flame barrier

FIG. 5 shows a schematic illustration of a flame burning the flowing gason the outlet side of the flame barrier in the case of a first gap

FIG. 6 shows a corresponding illustration for a flame on a second gap

FIG. 7 shows a perspective view of a second embodiment of a flamebarrier according to the invention

FIG. 8 shows a perspective view of a third embodiment of a flame barrieraccording to the invention.

The first embodiment of a flame barrier 10 according to the invention,illustrated in FIG. 3, comprises a cylindrical core 11, around whichturns 12, 13 are wound in the form of spirals. The turns 12, 13 eachconsist of a smooth metal strip 14 and a corrugated metal strip 15,which are wound up together. Wound up in the turns 12 is a metal strip15 having larger corrugations 16, while a corrugated metal strip 15′having smaller corrugations is wound up in the turns 13. Accordingly,continuous first passage gaps 17 having a larger gap cross section areformed in the turn 12 over the height of the flame barrier 10 (equal tothe width of the metal strips 14, 15, 15′), and second passage gaps 18having a smaller gap cross section are formed in the turns 12.

In the exemplary embodiment illustrated in FIG. 3 and FIG. 4, in eachcase a turn 12 having first gaps 17 and a turn 13 having second gaps 18alternate.

FIGS. 5 and 6 illustrate the situation in the case of a critical volumeflow for the first gaps 17 in the turn 12. Since the critical volumeflow has been reached, the flame 7 is already burning within the gap 17and thus leads to the metallic boundaries of the gap 17 heating up. Bycontrast, the same volume flow in the second gaps 18 leads to a highergas velocity, so that the flame 7 burns outside the second gap 18, sothat the metallic boundaries of the gap 18 remain well cooled. Since theboundaries of the gaps 18 are in direct or indirect metallic contactwith the boundaries of the gaps 17, dissipation of the heat from thehotter gaps 17 to the cooler gaps 18 takes place, so that effectivecooling of the first gaps 17 is carried out by the second gaps 18.

In the exemplary embodiment of a flame barrier 20, illustrated in FIG.7, in each case two turns 13 having second gaps 18 are arranged betweentwo turns 12 having first gaps 17. This arrangement leads to moreintensive cooling of the boundaries of the first gaps 17 of the turns12.

In the further exemplary embodiment of a flame barrier 30, illustratedin FIG. 8, considerably more turns 12 having first gaps 17 are providedthan turns 13 having second gaps 18. However, the frequency of the turns13 having second gaps 18 increases toward the core 11 of the flamebarrier. For example, in each case one turn 12 is arranged beside a turn13 in the core region of the flame barrier 30. After approximately onethird of the radius, in each case three turns 12 and one turn 13 follow,while in the outer region of the flame barrier 30 only turns 12 areprovided.

With this design, account is taken of the fact that disk-like flamebarriers 30 regularly heat up more intensely in the core than in theouter region. Account is taken of this by the intensified arrangement ofthe turns 13 in the inner region relative to the turns 12, in order toeffect improved cooling in the inner region of the flame barrier 30.

It is clear to those skilled in the art that numerous modifications tothe exemplary embodiments illustrated are possible within the claimedinvention. In all cases, improved cooling of the flame barriers 10, 20,30 is effected without seriously increasing the flow resistance andtherefore the cross-sectional area needed for the flame barrier 10, 20,30.

1. A flame arrestor for a flowing explosive gas, having a disk structurewith a front face and a back face, the disk structure comprising:structure forming multiple concentric rings of first gas passages, abouta longitudinal axis in a flow direction, extending from the front faceto the back face, said first gas passages each having a cross-sectionalarea, normal to the flow direction, larger than a given value; andstructure forming at least one ring of second gas passages, said ringbeing substantially concentric with said multiple concentric rings offirst gas passages, said second gas passages extending in the flowdirection and each having a cross-sectional area, normal to the flowdirection, less than the given value, wherein said multiple concentricrings of first gas passages and said at least one ring of second gaspassages are arranged in an alternating pattern, such that said at leastone ring of said second gas passages surrounds at least one ring of saidfirst gas passages.
 2. The flame arrestor of claim 1, wherein saidstructure forming at least one ring of second gas passages formsmultiple concentric rings of said second gas passages, and wherein saidmultiple concentric rings of first gas passages and said multipleconcentric rings of second gas passages are arranged in an alternatingpattern of each of said concentric rings of first gas passages beingbetween and concentric with rings of said second gas passages.
 3. Theflame arrestor of claim 1, wherein the structure forming said multipleconcentric rings of first gas passages includes a first corrugated metalstrip wound spirally with a smooth metal strip, and the structureforming said at least one ring of second gas passages includes a secondcorrugated metal strip wound spirally with a smooth metal strip, thefirst corrugated metal strip having larger corrugations than the secondcorrugated metal strip.
 4. The flame arrestor of claim 1, wherein saidstructure forming at least one ring of second gas passages formsmultiple concentric rings of said second gas passages, and wherein theratio of the number of rings of said second gas passages to the numberof rings of said first gas passages varies over the area of the flamebarrier.
 5. The flame arrestor of claim 4, wherein the ratio of thenumber of rings of said second gas passages to the number of rings ofsaid first gas passages decreases along the radial distance from saidlongitudinal axis.
 6. The flame arrestor of claim 1, characterized inthat the second gas passages gaps all have the same gap cross sections.7. The flame arrestor of claim 1, wherein at least one of the second gaspassages has a cross sectional area different from a cross sectionalarea of another of said second gas passages.
 8. The flame arrestor ofclaim 1, wherein the first and second gaps are formed with the same gaplengths.
 9. The flame arrestor of claim 1, characterized in that thecross-sectional area of the second gas passages is not greater than 50%of the cross-sectional area of the first gas passages.